As materials for housings for laptop PCs and portable devices, unreinforced or fiber-reinforced flame retardant ABS and flame retardant PC-ABS have been exclusively used heretofore.
Recently, weight reduction and thickness reduction of devices have been strongly demanded and it has also been required for it to endure impacts and loads when carried in a bag. Therefore, it has become necessary to reduce the thickness and weight of the housing and to impart high impact resistance thereto. Thus, high rigidity and impact properties are required from a resin used as the material of the housing.
Also, the housing for these devices require electromagnetic wave shielding properties (hereinafter referred to as EMI shieldability). The method of imparting EMI shieldability includes, for example, a method of using a resin containing about 30% by weight or more of carbon fibers, a method of inserting a metal foil or a metal plate upon in-molding or assembly of a product, and a method of subjecting to electroless plating or conductive coating.
Among conventionally used materials, unreinforced flame retardant ABS and flame retardant PC-ABS cannot cope with recent thickness reduction because of poor rigidity. A glass fiber-reinforced material is insufficient in balance between rigidity and weight. In a carbon fiber-reinforced material, when using a resin containing about 30% by weight or more of carbon fibers, EMI shieldability can be obtained. However, there arises a problem in that carbon fibers are expensive and the material containing carbon fibers in an amount of less than 30% by weight must be subjected to another treatment so as to impart sufficient EMI shieldability. Large content of carbon fibers causes a problem in that the appearance of a resin molded article made of the material becomes poor.
Although laptop PCs and portable devices contain sources of heat, such as CPUs, a calorific value tends to increase because of the high density thereof. Also, because of thickness reduction of the housing, heat removal is considered to be an important problem.
A material having high thermal conductivity is preferably used. as the material of the housing to remove heat. Since a resin material generally has low thermal conductivity, other measures must be adopted to remove heat in order to use a housing made of the resin.
From an environmental point of view, it has been recently required to use a flame retardant material free from halogens such as chlorine or bromine, which copes with the trend toward German and Swedish Ecolabeling.
Under these circumstances, housings for laptop PC and portable devices are required to be light weight, have thin walls, high rigidity, high impact resistance, high thermal conductivity, EMI shieldability, and be mass productible, and also require the use of an environmentally friendly material.
As a method of obtaining a device housing which is light weight, and has high rigidity, good thermal conductivity, and low cost, Japanese Unexamined Patent Application, First Publication No. 2000-349486 proposes a housing wherein the surface of a resin molded article obtained by molding of a thermoplastic resin is subjected to metal plating.
However, the technique disclosed in Japanese Patent Application, First Publication No. 2000-349486 is considered to be insufficient from the following point of view with respect to the production of a housing which meets all performance requirements described above.
For example, in Example 5 of the publication, a halogen-free phosphate ester flame retardant is used as a flame retardant, but it has low molecular weight. Therefore, the flame retardant has a low melting point and is liable to vaporize (gasify) at high temperatures, and thus large amounts of gas are evolved during molding. Consequently, there arise problems in that evolved gas contaminates the mold surface and is deposited on the mold parting plane (mold deposit), resulting in poor productivity, and problems such as poor formation of a plating layer of plated parts, and poor appearance.